Thin ferrite films have advantageous properties, such as absorption of electromagnetic radiation. However, it is well known that the properties of conventional ferrite materials are seriously degraded for frequencies above 1 GHz. There are numerous applications for materials or structures that provide the properties of a thin ferrite film at frequencies above those conventionally available.
Metamaterials are generally multi-component structures that can provide advantageous physical properties compared with uniform bulk materials. Such structures are also sometimes called engineered materials. A metamaterial ferrite is a metamaterial providing the properties of a ferrite film. It would also be very useful to be able to design metamaterials so as to provide desired permeabilities at given frequencies, particularly above 1 GHz.
A frequency selective surface (FSS) typically comprises a two-dimensional, doubly periodic, lattice-like structure of identical conducting elements. An FSS may also comprise an array of dielectric elements (possibly slots) within a conducting screen. A frequency selective surface (FSS) located close to a PEC (perfect electrical conductor) ground plane exhibits high impedance within narrow frequency bands, and is referred to as a high impedance frequency selective surface (HZ-FSS). Within these narrow frequency bands, the HZ-FSS structure functions as artificial magnetic conductor (AMC), having a reflection amplitude near unity and a surface reflection phase of zero degrees. An AMC can be used to suppress transverse electric and transverse magnetic surface waves. The term AMC is also used to refer to structures capable of acting as an artificial magnetic conductor at one or more frequencies.
FSS and AMC structures are described in U.S. Pat. No. 6,218,978 to Simpkin et al., U.S. Pat. No. 6,411,261 to Lilly, U.S. Pat. No. 6,483,481 to Sievenpiper et al., and U.S. Pat. No. 6,512,494 to Diaz et al.
FSS and AMC structures are of interest to antenna design. For example, U.S. Pat. No. 6,597,318 to Parsche et al. discloses a printed circuit antenna comprising a dielectric substrate disposed on a conductive ground plane. U.S. Pat. No. 6,262,495 to Yablonovitch et al. describes structures for eliminating surface currents on antenna surfaces. Also, U.S. Pat. No. 6,661,392 to Isaacs et al. discloses resonant antennas using metamaterials.
Patents and patent applications referenced in this disclosure are incorporated herein by reference.